A conventional electric motor is generally described in the U.S. Pat. No. 5,977,666, and the structure and manufacture of commutators are generally described in U.S. Pat. No. 6,242,839 and U.S. Pat. No. 4,872,255.
The functionality of the electrodynamic machines such as motors and generators are based on proper commutation. The proper flow and distribution of the electrical energy to the armature windings is commonly solved by the use of commutators and brushes. In a permanent magnet direct current brush motor (PMDC BM) assembly the commutator bar segments are electrically connected to the armature windings and at least one pair of brushes (one positive and one negative) are in contact with the surface of the commutator bars. The armature windings are placed onto the core of the armature in a pattern relative to the commutator hooks. The winding pattern and the style of the winding are determined based on the number of magnetic poles (magnet angle) of the electric machine. Furthermore, the brushes are positioned relative to the permanent magnets of the electrical machine. Then, the electrical current is conveyed from a given power source through at least one positive brush to the armature windings. The current conducting windings under the magnetic fields will generate rotational torque on the armature at a desired angular speed to produce mechanical power.
For adequate commutator and brush interface, the commutator surface is machined after the armature winding is completed. Although the best process is selected to perform this operation, there is a certain force (tensile and compressive) transferred to the anchoring system of each commutator bar. Therefore, the anchoring configuration of each bar must be robust enough to withstand the machining forces with acceptable surface conditions such as TIR (Total Indicted Run-out) and BTB (Bar to Bar).
Since the proper function and durable life of an electric machine depends mainly on the robustness of the commutation interface components such as the commutator and brushes, a good motor configuration must ensure that the commutator bars have sufficient thickness and robust anchoring features. More specifically the commutator must withstand high rotational speeds, tensile and compressive forces from the surface cutting operation and thermal and mechanical stresses that may occur during the life of the product.
The current production commutators work well in low power ranges used by most of the auto manufacturers. However, based on forecasts of higher power motor requirements new validation testing was performed using the current commutator and the test results indicated that the current configuration did not provide adequate anchoring for higher power applications. Therefore, there is a need to improve the anchoring structure of the commutator bars for higher power applications.